1. Field of the Invention
The present invention relates to a flat type piezoelectric ultrasonic motor for generating a rotation force to a rotor by an ultrasonic vibration, and more particularly, to a flat type piezoelectric ultrasonic motor equipped with a rotor, a vibrator and piezoelectric plates respectively arranged on quartered surface areas of the vibrator, and driven in such a way that the rotor is rotated by the vibrator vibrated by different-phased alternating currents applied to the quartered surface areas, thereby making it possible to simplify the piezoelectric plates' shape, minimize its size and enhance its driving efficiency.
2. Description of the Related Art
In general, a conventional piezoelectric ultrasonic motor is also called a traveling-wave type motor, a surface-wave type motor or a surfing type motor, and is driven by superposing two different-phased standing waves.
FIG. 1 illustrates a structure of such a conventional piezoelectric ultrasonic motor.
Referring to FIG. 1, a piezoelectric ultrasonic motor 200 is constructed in such a way that a plurality of piezoelectric plates 220 are arranged in a ring type on a lower surface of a ring type rotor 210 as shown in FIG. 1(A), or that a plurality of piezoelectric plates 240 are arranged in a ring type on an inner surface of a ring type rotor 230 as shown in FIG. 1(B).
As shown in FIG. 1(C), the piezoelectric ultrasonic motor 200 is operated in such a way to alternately induce polarizations in a plurality of electrodes of the ring type piezoelectric plates 220 and then apply different-phased resonant-frequency voltages to the electrodes thereby to generate elliptical-locus traveling waves on surfaces of the ring type piezoelectric plates 220.
However, it is difficult to manufacture the ring type piezoelectric plates 220 and to induce a plurality of polarizations in the ring type piezoelectric plates 220.
Also, stresses are concentrated on boundary surfaces between the electrodes of the ring type piezoelectric plates 220 during the operation of the motor 200, whereby such a stress concentration incurs cracks and breaks in the plates 220.
Moreover, it is difficult to miniaturize the motor 200 because the plates 220 have a plurality of electrodes and polarizations.
In the meantime, a conventional ultrasonic motor device generating linear motion by ultrasonic vibrations is disclosed in Japan Patent No. JP2004-088815.
FIG. 2 illustrates a structure of such a conventional ultrasonic motor device operated in such a way that a control range of a driving speed is expanded in a low-speed range.
Referring to FIG. 2, an ultrasonic motor device 300 is constructed to include a motor 310A having a vibrator 311 and a moving unit 312, power sources 316A and 316B, a phase controller 317 for diverting phases of driving voltages outputted from the power sources 316A and 316B, and a preloader 318 for supporting the vibrator 311 and pressing the moving unit 312 with a given force.
In the ultrasonic motor device 300, upper piezoelectric elements 314A and 314B are attached on the upper surface of the vibrator 311 with their longitudinal axes being aligned, and lower piezoelectric elements 314C and 315D are attached on the lower surface of the vibrator 311 with their longitudinal axes being aligned in parallel to those of the upper piezoelectric elements 314A and 314B. A driving voltage from the power source 316A is applied to the diagonally-opposed elements 314B and 314C and another driving voltage from the power source 316B is applied to the diagonally-opposed elements 314A and 314D, whereby the vibrator 311 is vibrated and thereby the moving unit 312 drivingly connected to the vibrator 311 is linearly moved.
Also, a moving speed of the moving unit 312 can be changed by a phase change of the driving voltages, or by a load change of the preloader 318.
However, the moving unit 312 can be moved only linearly, but not rotatively.